Pheophytin
or Pheo is a chlorophyll molecule lacking a central Mg2+ ion which
serves as the first electron carrier intermediate in the electron transfer pathway
of photosystem II in plants and the photosynthetic reaction center RC P870 found
in purple bacteria. In both PS II and RC P870, light drives electrons from the
reaction center through pheophytin, which then passes the electrons to either
a quinone (QA) in RC P870 or plastoquinone in PS II. Only chlorophyll
of the P680 reaction center in photosystem is capable of transferring an electron
to pheophytin. The overall mechanisms, roles, and purposes of the pheophytin molecules
in the two transport chains are analogous to each other.. .
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